Intermediates in nucleophilic aromatic substitution. Part XIII. Kinetic and proton magnetic resonance investigations of the interaction of methoxide ions with 1-methoxy-2,4,7-trinitronaphthalene

Abstract

The rate constants (k₁) for the formation of the 1,1-dimethoxy-complex of 1-methoxy-2,4,7-trinitronaphthalene in methanol at 7·95, 15·35, and 25·00 °C have been determined spectrophotometrically by following the increase in absorbance at 480 nm as a function of time in 5·0 × 10^–5M solutions of 1-methoxy-2,4,7-trinitronaphthalene in the presence of methoxide ions [(0·56–14·0)× 10^–3M]. The rate constants (k_–1) for the decomposition of the complex have been determined directly at the same three temperatures by following the decrease in the absorbances of dilute methanolic solutions of the isolated complex. From these values the equilibrium constant, and the energy and entropy of activation for the formation of the complex (1·09 × 10⁵ l mol^–1, 13·3 kcal mol^–1, and –8·0 cal mol^–1 K^–1, respectively) and the energy and entropy of activation for its decomposition (20·3 kcal mol^–1 and –7·2 cal mol^–1 K^–1) have been calculated. The stability of this complex is discussed in comparison with other Meisenheimer complexes. The structure of the 1,1-dimethoxy-complex of 1-methoxy-2,4,7-trinitronaphthalene has been established from ¹H n.m.r. spectra of both the isolated and the complex generated in situ. The ¹H n.m.r. parameters of the complex and its parent ether are discussed and contrasted with those for other naphthalene complexes.